The present invention relates to a computer assisted video surveying and method therefor.
Typical land based surveying methods involve measuring distances from a certain known point and noting the bearing and angle of declination or inclination of the sighting tool between the known point and a plurality of measurement sites. The data is generally obtained manually and then transferred to graphs, charts and maps of the surveyed area. The manual gathering of data is time consuming, labor intensive and hence costly. An aerial survey encounters the same problems as the land based manual survey.
U.S. Pat. No. 4,396,942 to Gates discloses a method and an apparatus for obtaining a video survey of an area. The system utilizes a video camera mounted on a vehicle. In one embodiment, a grid is placed on the front end of the vehicle in the field of view of the camera. A measurement of an object in the field of view is taken at a control location. The video film is played back and when image of the measured object falls within an overlay grid placed on the video monitor, the grid is marked such that the marked grid represents the actual size or dimension of the measured object. Accordingly, all objects displayed on the monitor and falling between the markings on the overlay grid have similar measurements compared with the known object as long as the video camera has not moved with respect to the vehicle. In another embodiment, the overlay has multiple distance scales which the Gates '942 disclosure states can be mathematically computed based upon a predetermined control position of the camera, the height of the camera, the focal length of the camera and the field of view of the camera. It has been found that additional parameters must be incorporated into the system in order to obtain a highly accurate video survey. Also, no precise provision is made for measuring objects distant from the point of observation and not directly framed by the grid on the front of the vehicle. If the object to be measured does not fall within the grid, it cannot be measured.
U.S. Pat. No. 3,909,519 to Page, Jr. discloses a measuring system employing a television camera tube which captures a video image of an object under observation. Reference lines are generated on a video monitor by counting pulses tracking the video signal stream. A plurality of uniformly spaced scale markings are scribed onto the camera tube which provides a reference baseline which is proportional to the object being measured by the video system. To calibrate the system a measurement is made of an object of known dimensions and the size of the video image of the object under observation is calculated based upon the correlation between the known object and the video image size of the object under observation. No provision is made for measuring objects in the field of view distant from the known object or correcting for depth perception of the objects to be measured. Accordingly, the Page system cannot correct for the size of objects distant from the know object.
U.S. Pat. No. 2,616,177 to Bazhaw discloses an apparatus and method of surveying elevations utilizing a still, photographic camera, with scale markings on its lens, and a rod having scale markings and an upper and lower target. The rod is placed in the field of view of the camera, the camera is held level, i.e., at 0 degrees declination, and a photo is taken. The rod is then moved a certain measured distance from the first position and another picture is taken. With these two pictures, the elevation differential between the two rod locations can be computed using image distances from (1) the lens scale to a point on the rod and (2) two points on the rod and using the focal length of the camera lens. The distance from the camera to the rod is similarly computed. Importantly, the camera must be level or set at a 0 degree declination.
U.S. Pat. No. 4,005,932 to Gates discloses a photogrammetric method and apparatus to eliminate relief distortion from aerial photographs and to produce orthostereoscopic photos of topography.
U.S. Pat. No. 4,148,583 to Gates discloses an orthostereoscopic plotter from which contour maps can be produced from orthostereoscopic slides or prints.
U.S. Pat. No. 4,659,959 to Lees et al. discloses a passive range measurement system which obtains stereo image pairs of a terrain. The image pairs are placed in registry by targeting a single object in both images. To register the two images, the displacement of the camera from point A, the first image observation location, to point B, the second image observation location, must be known. This is accomplished by using the velocity of the airplane and other measured movement parameters.